Starting in the late 1980s, along with the development of the Micro Electro Mechanical Systems (MEMS) technology, some semiconductor devices such as many sensors became a major direction of future development because microminiaturization and batch production of such devices had been realized.
According to the current technology, multilayer materials are usually deposited at a single wafer and then fixed electrodes of MEMS devices and movable electrodes suspended in cavities of the MEMS devices may be further formed. Practical studies indicate that deposition of multilayer materials on a single wafer mentioned above may induce considerably large stress and if the stress is not completely released, it may result in bow of the wafer used to form the MEMS devices. Specifically, the large stress in the multi-layer structure leads to deviation of the center point of the MEMS device from the surface of the reference plane away from the device region. The deviation is known as wafer bow. If subsequent processes are required to be performed on the bowed wafer, a mechanical arm is needed to grab the wafer. The principle of grabbing a wafer using a mechanical arm in the current technology is that after the wafer is placed on the loading surface of the mechanical arm, the interface between the wafer and the arm is pumped and the wafer may then be held on the mechanical arm by vacuum generated at the interface. A bowed wafer may cause a failure of the vacuum at the interface between the wafer and the mechanical arm, thus interrupts the fabrication process.
In view of the above, the present disclosed invention provides a new fabrication method for MEMS devices to avoid the abovementioned problem in the fabrication process due to wafer bow.